In certain types of chemical processes, an input slurry stream is fed to a process zone wherein countercurrent particulate solids separation and washing are carried out. Such an input slurry stream is characteristically subject to great variability in composition and physical characteristics. For purposes of process control, it would be highly desirable to be able to continuously automatically and accurately monitor the condition of process streams involved in such a process zone which streams are derived from such an input slurry stream.
Means and techniques heretofore known in the art for continuously, simultaneously, and accurately monitoring streams in such a countercurrent process have generally been unstable, inaccurate, cumbersome, and expensive. Typically, in order to obtain accurate results, it was necessary to employ measurement techniques which could not be effectuated on an immediate basis. Commonly, a series of on-line samplings, followed by a series of off-line analytical procedures, resulted in an appreciable time gap between the actual process stream condition and the production of data representative of such condition. Typically, output streams rather than input streams were used as a basis and source for instantaneous process condition measurements.
A basis for an improved control technique for such a countercurrent system appears to lie in the method of measuring process stream parameters. In this connection, it has previously been proposed to measure the conductivity of an electrolyte with an electrodeless probe using two torroidal ferromagnetic cores in a solution. An oscillator is connected to a winding on one of the cores and a winding on the other core is coupled to a detecting circuit; see Relis U.S. Pat. No. 2,542,057. Recently, the Relis principles have been extended so as to provide an electrodeless conductivity measuring system which does not require external compensating apparatus for residual coupling between primary and secondary windings; see Gross U.S. Pat. No. 3,806,798. So far as is now known, no one has heretofore employed a pair of electrodeless conductivity probes for differential, preferably continuous, conductivity measurement in an input process fluid as a part of a process control technique.